Field of the Invention
The present invention relates to a wire electrical discharge machining apparatus, a wire electrical discharge machining system, a power supply apparatus, a wire electrical discharge machining method, and a method of manufacturing a semiconductor substrate.
Description of the Related Art
Hitherto, a wire saw is known as an apparatus for cutting a silicon ingot into multiple thin slices. In recent years, there is a technology for cutting a workpiece into thin slices by using a wire electrical discharge machining technology. For instance, Japanese Patent Application Laid-Open No. 2012-200802 discloses a technology for machining multiple ingots by using a multi-wire electrical discharge machining apparatus.
Japanese Patent Application Laid-Open No. 2012-200802 discloses a technology in which rotating electrodes and two ingots are arranged alternately so that distances between three rotating electrodes and centers of two cutting wires are equal to each other, and two machining voltages are applied individually to the ingots in order to supply a uniform electrical discharge machining current to the individual ingots.
With this apparatus structure, it is possible to realize the uniform machining current flowing in a direction to the two ingots at a shortest distance from the electrodes. However, a machining current also flows around from each electrode to a far side between the electrodes, i.e., the current also flows in the opposite direction. Therefore, a machining current that does not contribute to the cutting of the two ingots flows in the wire.
Further, in Japanese Patent Application Laid-Open No. 2012-200802, when the wire electrical discharge machining of two ingots is performed as a batch process, because the machining voltage is set individually for each ingot, the machining voltage and a feeding amount of a workpiece can be controlled individually for each ingot. However, the number of control units for applying machining voltages to the two ingots is increased, and hence the control units are complicated, resulting in an increase of apparatus cost.